Simultaneous removal of heavy metals from aqueous solutions by pineapple crown and avocado peel hydrogel composites

BACKGROUND AND OBJECTIVES: Heavy metal contamination from industrial wastewater remains a global concern. Biomass waste still contains active compounds that can be processed into useful materials. The study objectives were to address both problems by synthesizing composite hydrogels from pineapple crowns and avocado peels for the simultaneous adsorption of lead(II), cadmium(II), and copper(II) from aqueous solutions.METHODS: Composite hydrogels were synthesized using free radical polymerization using pineapple crown biochar and avocado peel biochar as grafting substrates. The material was characterized using Fourier transform infrared spectroscopy, scanning electron microscopy-energy dispersive x-ray spectroscopy, Brunauer-Emmett-Teller, and hardness testing to determine its physicochemical properties. The adsorption process uses a batch system in a solution containing lead, cadmium, and copper ions simultaneously at potential ۴ to ۶ and a temperature of ۲۶ degrees Celsius with a speed of ۱۲۵ revolutions per minute for an operating time of ۳۰۰ minutes. The kinetics of adsorption were evaluated using the pseudo-first-order and pseudo-second-order models, and the model fit was based on the coefficient of determination value and the correlation.FINDINGS: Both hydrogels demonstrated mesoporous structures with high specific surface areas (square meters per gram) of ۷۶۷.۶۱ for pineapple crown composite hydrogel and ۸۰۲.۴۱ for avocado peel composite hydrogel, along with rich functional groups such as hydroxyl, carboxyl, alkyl, nitrile, and carbonyl groups that facilitate chemisorption. The avocado peel composite hydrogel showed the highest adsorption capacity (milligrams per gram), which was ۰.۵۶ for lead, ۰.۴۳ for cadmium, and ۰.۴۱ for copper. These results were better than the performance of the pineapple crown composite hydrogel. Adsorption kinetics were well described by the pseudo-second-order model, with coefficient of determination values from ۰.۹۱ to ۰.۹۸ for composite hydrogel.CONCLUSION: The performance of avocado peel composite hydrogels has improved compared to that of pineapple crown composite hydrogels, which is due to better porous accessibility and the presence of functional groups. These results confirm the importance of biomass selection and synthesis conditions. Although the resulting adsorption capacity is lower than developed adsorbents, this study provides advantages in terms of sustainability, low cost, and the accessibility of local raw materials, making it highly promising for sustainable wastewater treatment.

کلیدواژه ها:

Adsorption kinetics ، Biomass waste ، Composite hydrogel ، Simultaneous heavy metal removal ، Wastewater treatment